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Cavitation resistance of chromium-nickel tool steels obtained by hot isostatic pressing
No full textThe paper presents the results of research into the cavitation resistance of tool steels obtained by
the process of hot isostatic pressing. The compositions of the powder mixture for pressing, as
well as the parameters of the HIP process, primarily temperature and pressure, were investigated.
The pressing temperature ranged from 1000-1150°C, the pressing pressure was 100 to 300 MPa,
and time was 3-4 hours. These steels are used for the production of equipment parts in
metallurgy, mechanical engineering and mining. The cavitation resistance of three series of steels
with different nickel and chromium content was tested using the ultrasonic vibration method with
a stationary sample according to the ASTM G32 standard. The reduction of the nickel content in
the composition of the steel has a favorable effect on the development of the martensitic
transformation and the increase in the hardness of the steel. The presence of chromium improves
the mechanical properties and chemical stability of steel. The obtained cavitation speeds below
0,11mg/min indicate a good cavitation resistance of the samples and the possibility of application
in conditions of exploitation where the presence of cavitation, corrosion and wear is expected
Development of prediction methods required for stability assessment of river-sea ships
No full textThe natural roll frequency and the effective wave slope coefficient are two essential parameters for dynamic ship stability assessment. While these parameters may be calculated based on first principles, or even experimentally, simplified semi-empirical methods still represent a more practical approach for everyday use. However, there is a lack of adequate methods for river-sea ships. Therefore, the paper presents regression formulae for added inertia, for use in the prediction of natural roll frequency, and for effective wave slope coefficient at the natural roll frequency. The performance of the developed formulae is assessed with respect to the original data they were derived from, as well as with respect to a test dataset. Furthermore, for the prediction of natural roll frequency, a comparison is carried with an existing semi-empirical method specifically intended for inland vessels and river-sea ships, showing that the formulae proposed in the paper could lead to significant improvements in prediction capabilities
WAVELET TRANSFORM PACKET FOR SIGNAL ANALYSIS USING STANDARD DEVIATION AND SIGNAL SPECTRUM
No full textThe paper presents the research results and the possibilities of applying the standard deviation and amplitude spectrum for chatter vibration detection using the wavelet transform packet as a tool for signal decomposition that was recorded during machining. An analysis of the signal spectrum was additionally performed, which is represented by a spectrogram. Two experiments were performed, where the cutting force signal and acceleration signal, recorded during the machining processes, were analyzed. The recorded signals were decomposed using the wavelet transform packet with the mother wavelet 'db4', and then the standard deviation in the time domain and the amplitude spectrum in the frequency domain were calculated for each level of the decomposed signal. The application of wavelets in this study is intended to enable a better assessment of the quality of standard deviation and amplitude spectrum in chatter vibration detection
ULTIMATE STRENGTH OF INLAND VESSELS: RHINEMAX CLASS
No full textWhile the ultimate strength of sea-going ships is extensively explored in scientific literature, its practical application in industry remains limited. On the other hand, rules and regulations for ship construction have already incorporated detailed procedures for ultimate strength assessments in publications such as the Common Structural Rules for Bulk Carriers and Oil Tankers (CSR BC & OT). In contrast, inland waterway vessels (IWV) ultimate strength calculations are not applied in practice at all. Scarcity of literature data on this subject is evident, except for a handful of case studies focused on single vessels. Moreover, due to unharmonized and underdeveloped rules and regulations for IWV, their much older age compared to sea-going ships, and a lower inland waterway transport industry awareness regarding structural safety, IWV can be more prone to sudden collapse of hull girder. In fact, shallow water operations and the presence of bridges along the waterway govern the shallow draught of IWV, their higher length to breadth and length to height ratio than those of sea-going ships, making them vulnerable to the longitudinal strength issues. Recordings show that hull girder collapses on river occurs due to chain events of the various phenomena: grounding, improper overhauling of grounded ship, overloading, hull modulus diminished by severe corrosion and wear, improper maintenance. Therefore, the main aims of this work are to identify gaps in rules and regulations regarding ultimate strength assessments of IWV and to perform benchmarking analysis of ultimate strength for a class of similar IWV (i.e, Rhineclass, the largest on the river Rhine). For that purpose, a progressive-collapse analysis defined in IACS CSR BC & OT is used, which we automated in Python. Moreover, we checked the sensitivity of ultimate strength results by selecting two contemporary approaches for the calculation of ultimate strength of stiffener with attached plating: a) Jonson- Ostenfeld (J-O) and b) Paik-Thayamballi (P-T). Furthermore, our investigation seeks to determine whether there are differences in collapse sequences between IWV and the majority of sea-going ships. Results show that the abovementioned approaches lead to the difference on ultimate strengths of selected ships up to 5% meaning that each one of them will estimate similar ultimate bending moments. Moreover, findings show that Rhineclass inland vessels will firstly collapse as a hull girder before reaching the first-yield bending moment, which is contrary to sea-going ships case. Analyzed IWV will never yield, as their ultimate collapse is completely governed by buckling
ULTIMATE STRENGTH OF CORRODED HULL
No full textDuring the preliminary design of ships, almost all structural assessments are based on prescribed rule-based formulas and occasional direct calculations such as longitudinal strength, buckling and finite element analysis. Consequently, the maximum stress of the structure resulting from the critical loading is evaluated with respect to rule-prescribed allowable stress, which is lower than the yield stress of the material. This means that the strength of the ship is assessed only considering its predicted loading scenarios, original (as-built) scantlings and within its elastic response. However, the strength of the ship with respect to excessive (unpredicted) loadings, such as vertical bending moment and corroded scantlings is generally neglected. Fortunately, IACS has been developing ultimate strength procedures in its Common Structural Rules for Bulk Carriers and Oil Tankers (CSR BC & OT) based on progressive-collapse analysis (PCA) and nonlinear finite element method (NLFEM). Therefore, this work aims to present the ultimate strength assessments for a bulk carrier, in intact condition (no corrosion) and in corroded conditions of various severities and types. Moreover, an actual levels of ultimate strength reductions of the hull due to ageing of structural elements are delivered, proving that it has an important effect on structural integrity of the ship
The impact of sintering parameters on the physical properties of ceramic samples obtained by andesite basalt powder
No full textContemporary development of materials prioritizes environmentally friendly and lightweight materials with outstanding physical-mechanical properties fabricated from low-cost natural raw materials that are readily available. In this regard, basalt has emerged as a leading contender. Basalt is a natural igneous rock that can be found in large quantities worldwide, including in Serbia. It is classified as a non-toxic and eco-friendly material, which makes it highly suitable for wide use in construction and industry.
Andesite basalt aggregate from the "Donje Jarinje" site in Serbia was used to produce high-density ceramic materials. Powder metallurgy was used as a technological process. This technology process involved dry grinding (30 min), manual homogenization (10 min), cold uniaxial pressing (50 MPa), isostatic pressing (230 MPa) of powder, and sintering. Sintering was performed at temperatures 1040, 1050, 1060, 1070 and 1080 °C for 1 hour in the air. This research determined that the highest density of ceramic material from andesite basalt powder is obtained after 1 hour of sintering in the air at 1060 °C. The sample achieved a relative density of 99.5 %. The shrinkage after sintering was 12.8%, while the weight loss was 2.9 % [1]. It is essential to point out that the samples' colour changed after sintering, which was observed by visual control. Due to sintering in the air, hematite formations occurred in the samples, which
was confirmed by XRD analysis. With increasing temperature, the colour of the sintered samples changed from light reddish-brown to dark brown. The colour of the sample as a parameter can enable easier monitoring of the production process and indicate the density of the material, i.e. the quality of the manufactured part
Experimental analysis of fracture behavior of biomaterials for orthopedic applications
No full textThe experimental tests presented in this work aim to identify and analyse factors influencing the mechanical behaviour of biomaterials for orthopaedic applications, with a crack-type error that leads to failure due to fatigue in real operating conditions. The study involved experimental tests and fracture resistance analysis of two selected biomaterials 316L stainless steel and Ti-6Al-4V alloy, performed using standard fracture mechanics tests.Standard procedures were conducted to determine the fracture toughness KIc at plain strain conditions, and specimens with notches and prescribed fatigue crack lengths were used for this purpose. Compact tension specimens C(T) defined by the ASTM E399-06 and ASTM E1820-08 standards were chosen for the experimental research. After obtaining the experimental Kc values, parameters such as CTODc or Jc were determined using the same standard tests and procedures according to the ASTM E1820 standard. Laboratory tests were performed on test specimens extracted from S316L steel plates and Ti-6Al-4V titanium-based alloy plates to determine the critical stress intensity factor, KIc.
The influence of structural heterogeneity and mechanical properties of biomaterials during exploitation primarily manifests in the position of the fatigue crack tip and the properties of the surrounding area where fracture occurs and propagates. The results of this experimental research can be applied to evaluate the mechanical behaviour of biomaterials used in orthopaedic implants in the presence of crack-type defects, which are the most critical defects in structural materials. It can be concluded that understanding the behaviour of orthopaedic biomaterials under external physiological loads is crucial for ensuring implant integrity and safe operation. Research shows that the worst characteristics in relation to fracture toughness are titanium-based alloys, which also show a very high sensitivity to notches, however, it should be taken into account that when choosing materials for implants, the effects of material biocompatibility have a significant impact
Nerazarajuća metoda određivanja sklonosti prema interkristalnoj koroziji nerđajućeg čelika X5CrNi18-10 (AISI 304) zasnovana na merenju električne provodljivosti
No full textU ovom tehničkom rešenju prikazano je ispitivanje stepena senzibilizacije na interkristalnu koroziju (IKK) i električne provodljivosti nerđajućeg čelika X5CrNi18-10 (AISI 304), da bi se dobila odgovarajuća korelacija. Stepen senzibilizacije određen je metodom elektrohemijske potenciokinetičke reaktivacije sa dvostrukom petljom (DL EPR), dok je električna provodljivost merena komercijalnim uređajem (nedestruktivna metoda). Nakon elektrohemijskog nagrizanja u oksalnoj kiselini, mikrostruktura površine uzoraka analizirana je skenirajućom elektronskom mikroskopijom (SEM). U slučaju kada je stepen senzibilizacije bio veći od ~ 0,5%, dobijena je jasna linearna zavisnost električne provodljivosti i stepena senzibilizacije, dok za niže stepene senzibilizacije postoji veće odstupanje od linearnosti. Pomenuta korelacija je razmatrana s gledišta kinetike taloženja Cr-karbida duž granica zrna i formiranja Cr-osiromašenih oblasti različitog stepena u blizini granica zrna. Cr-osiromašene zone tokom anodne polarizacije pokazuju manju otpornost prema obrazovanju pitova. Prisustvo Cr-osiromašenih zona u blizini granice zrna i smanjenje sadržaja ugljenika u austenitnoj kristanoj rešetki utiče na povećanje električne provodljivosti nerđajućeg čelika
THE POST-PROCESSING METHOD FOR LARGE-SIZED PARTS PRODUCED USING SLA/mSLA TECHNOLOGY
No full textThe rapid development of additive manufacturing technologies over the past
10 years has led to their widespread use in all segments of product design and
production. Although these technologies are present in both industrial environments
and household settings, certain shortcomings are still noticeable and difficult to
eliminate. One of the main drawbacks of additive manufacturing technologies is the
working space, i.e., the maximum dimensions of the parts that can be produced. In the
case of FDM/FFF technology, the dimensions of the parts have not been as much of a
problem in recent years, and commercially available devices can produce large-sized
parts. However, in the case of SLA/mSLA technology, the working space is a limitation
that prevents the full potential of these technologies from being realized. This paper
focuses on finding ways to produce large-sized parts using SLA/mSLA technology on
commercially available devices. By segmenting parts into smaller sections and
following proper post-processing procedures, it is possible to create larger parts with
satisfactory mechanical properties
PROCENA RIZIKA ADITIVNIH PROIZVODNIH TEHNOLOGIJA PRIMENOM KINIJEVE METODE
No full textAditivne proizvodne tehnologije danas imaju veoma široku primenu, ne samo u industriji, već i u mnogim drugim privrednim granama. Njihova upotreba je veoma raznolika, s najčešćom primenom u izradi prototipova, odnosno, delova složene geometrije čija je izrada konvencionalnim tehnološkim postupcima otežana ili čak nemoguća. Ipak, uticaji aditivnih proizvodnih tehnologija na bezbednost i zdravlje ljudi još uvek nisu dovoljno istraženi. U ovom radu, primenom Kinijeve metode procene rizika, izračunate su osrednjene vrednosti rizika za različite tipove aditivnih proizvodnih tehnologija, uz pregled dostupnih standarda i zakonske legislative. Na osnovu sprovedene procene rizika, preporučene su i zaštitne mere za aditivne proizvodne tehnologije kod kojih su utvrđeni najviši nivoi rizik